Totally blind army ants carry out massive and highly organised foraging raids, apparently guided by chemical stimuli. Until now, this phenomenon has not been closely analysed. The existence of a trail pheromone in a postpygidial gland of an Aenictus species has been demonstrated and the substances identified as methyl anthranilate and methyl nicotinate The pheromone consists of two parts: a primer effect, caused by methyl nicotinate, which prepares workers to follow trails, but is not itself followed, and a releaser effect, due to methyl anthranilate, which causes trail-following only in conjunction with the primer substance.